ROMK K+ channels play essential roles in the baseline potassium (K+) secretion in cortical collecting ducts (CCDs). As exit pathways for K+ secretion, the density of ROMK channels in CCDs is regulated by dietary K+ intake. Variations of K+ intake alter surface abundance of ROMK channels by affecting clathrin-coated vesicle- mediated endocytosis of channels. These adaptive changes are important for maintaining K+ homeostasis during variations of dietary K+ intake. Pseudohypoaldosteronism type II (PHA II) is an autosomal-dominant disease characterized by hypertension and hyperkalemia. Mutations of WNK1 and WNK4 cause PHA II. WNK (with-no-lysine [K]) kinases are serine-threonine protein kinases with an atypical placement of the catalytic lysine. Recent studies suggest that increased endocytosis of ROMK (thus, inhibition of ROMK) may contribute to hyperkalemia in PHA II caused by mutations of WNK1 and 4. How mutations of WNK kinases cause endocytosis of ROMK is not known. The long-term goal of our research is to study the molecular mechanism for membrane trafficking of ROMK channel and its importance in renal physiology and diseases. For the next funding period, we will study the mechanism by which WNKs cause endocytosis and how mutations of WNKs in PHA II lead to increased endocytosis of ROMK. We will further examine the mechanism and role of WNKs in the regulation of ROMK by dietary K+ intake. These studies will help us understand how kidney adjusts K+ excretion to meet the balance of K+ intake. Project Narrative: Kidney plays an essential role in the control of blood potassium level by excreting excess potassium. Abnormality in blood potassium level causes irregular heart beat, muscle weakness, and sudden death. Our studies aim to understand how kidney excretes potassium in physiological and diseased states.